To increase fuel economy and/or performance in internal combustion engines, various devices and systems are known in the prior art for varying the opening and closing events of intake and exhaust valves from the eccentric rotary input of the camshaft. These devices and systems are known in the art as Variable Valve Activation (VVA) systems and require a selective supply of engine oil pressure to be provided to VVA devices, such as deactivating valve lifters (DVLs), switchable roller finger followers (SRFFs), and switchable hydraulic lash adjusters (SHLAs), as are all well known in the prior art.
Hydraulic pressure to these devices typically is provided via a solenoid-actuated three-port spool valve, having a pressurized oil supply port, a common port connected to the device, and an exhaust port for bleeding oil from the device. A spool valve typically comprises a tubular valve body containing a slidable spool connected to the solenoid that is shifted to open or close the various ports in the valve body. A significant drawback of such a spool valve is that it requires a high degree of precision in manufacture and assembly of the spool and the housing, and hence is costly to manufacture. Spool valves are also very susceptible to buildup of varnish on the spool and body walls, as well as to contamination from debris found in worn engine oil, both of which can lead to leaking and/or blowby within the valve, thus compromising performance.
What is needed in the art is an improved three-port valve that has high response, is less costly to manufacture, and is less vulnerable to varnish and contamination in use.
It is a principal object of the present invention to increase the reliability and working life of a three-port fluid control valve.
It is a further object of the invention to reduce the cost of manufacture of an internal combustion engine having VVA capability.